metamorphic

Foliated metamorphic rock, likely gneiss

Biotite–quartz–feldspar gneiss, possibly migmatitic gneiss

AI-generated identification · may be incorrect

Medium- to coarse-grained, gray rock with dark biotite-rich streaks, pale quartz/feldspar bands, and strong foliation; minerals have vitreous to pearly luster. Typical hardness is about 6–7 Mohs, with weak cleavage along mica-rich layers and specific gravity around 2.6–2.8.

Identified September 2, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when preexisting igneous or sedimentary rock underwent high-grade regional metamorphism, causing mineral recrystallization and compositional banding; commonly Precambrian to Paleozoic in age. The greenish vein may be epidote, chlorite, or another alteration mineral.

Uses & applications

Used as dimension stone, building aggregate, landscaping stone, and occasionally decorative slabs; intact attractive pieces have modest specimen value.

Geological facts

Gneiss commonly preserves alternating light and dark mineral bands produced by metamorphic segregation. It can resemble granite, but its minerals are aligned into visible foliation rather than randomly distributed.

Field identification & locations

Identify it by hard, interlocking quartz/feldspar grains and planar dark mica bands; a streaked, banded texture distinguishes it from massive granite. Common in ancient continental shields and mountain belts worldwide.